IS 5416-2: Methods of test for strength and stability of chairs and stools, Part 2: Determination of stability of chairs and stools

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IS 5416-2 (1988) : Methods of test for strength and
stability of chairs and stools, Part 2: Determination of
stability of chairs and stools [CED 35: Furniture]

Jawaharlal Nehru
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IS : 5416 ( Part 2 )- 1988

( Reaffirmed 2002 )

Indian Standard

METHODS OF TEST FOR
STRENGTH AND STABILITY OF CHAIRS

AND STOOLS

PART 2 DETERMINATION OF STABILITY OF CHAIRS AND STOOLS

( First Revision )

UDC 684-435:620-17

© Copyright 1989

BUREAU OF INDIAN STANDARDS

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

Gr 4 July 1989

IS I 5416 ( Part 2 ) - I9M

Indian Standard

METHODS OF TEST FOR
STRENGTH AND STABILITY OF CHAIRS

AND STOOLS

PART 2 DETERMINATION OF STABILITY OF CHAIRS AND STOOLS

( First Revision )

0. FOREWORD

0.1 This Indian Standard ( Part 2 ) ( First
Revision ) was adopted by the Bureau of Indian
Standards on 21 November 1988, after the draft
finalized by the Furniture Sectional Committee
had been approved by the Civil Engineering
Division Council.

0.2 This standard was first published in 1969
covering the methods of test for general purposes
of erect wooden chairs. Now this standard is being
issued in two parts. Part 1 covers methods of test
for determination of strength of chairs and stools
of all types.

0.3 This part ( Part 2 ) of the standard covers
methods of test for determination of stability of
chairs and stools.

0.4 In the formulation of this standard, conside-
rable assistance has been derived from BS 4875 :
Part 2 'Strength and stability of furniture Part 2
Methods for determination of stability of chairs
and stools; issued by the British Standards Institu-
tion.

0.5 For the purpose of deciding whether a parti-
cular requirement of this standard is complied
with, the final value, observed or calculated,
expressing the result of a test, shall be rounded off
in accordance with IS : 2-1960*. The number of
significant places retained in the rounded off value
should be the same as that of the specified value
in this standard.

♦Rules for rounding off numerical values (revised ).

1. SCOPE

1.1 This standard ( Part 2 ) prescribes the
methods for determination of stability of all types
of upright chairs and stools, easy chairs and tilting
and reclining chairs.

2. TERMINOLOGY

2.0 For the purpose of this standard, the follow-
ing definitions shall apply.

2.1 Stability — The ability to withstand over-
turning.

3. PRINCIPLE

3.1 The principle is to determine the stability of
an article by simulating the overturning forces
that occur in use and determining whether the
article overturns.

4. GENERAL REQUIREMENTS FOR TESTS

4.1 Test Loading — All loads and forces shall
be measured to an accuracy of ±5 percent.

Note — The tests may in certain cases be carried
out by means of loads or forces.

4.1.1 The apparatus used to apply seat loading
shall not restrain the article from overturning nor
hinder horizontal movement of the article when
the back force is applied.

4.2 Setting-Up of Furniture — The articles
shall be tested as delivered. Self-assembly furni-
ture shall be assembled according to instructions
supplied with the articles. If the article can be
combined in different ways, the most adverse
combination shall be used for each test.

5. APPARATUS

5.1 Means
Forces

of Applying Required Loads or

5.2 Means of Measuring Dimensions to an
Accuracy of ± 0-2 mm

5.3 Loading Point Template ( see Fig. 1 5 2

and 3 ) — It shall consist of two shaped members
fastened together by a pivot at one end. The con-
tours of the shaped surfaces are so devised as to
sink into the upholstery for a representative
distance under moderate loads. For this purpose,
the seat loading arm shall have a total mass of

I

IS t 5416 ( Part 2 ) - 1988

20 kg, applied through the seat loading point. The
apparatus is marked as shown in Fig. 1 so that
the template is positioned easily with the two
members at an angle of 90° to each other.

5.4 Floor

surface.

It shall comprise a level horizontal

5.5 Stops — These shall prevent the article from
sliding but not from overturning. Stops shall be
not higher than 12 mm except in cases where the
design of the article necessitates the use of higher
stops, where the lowest stop that will prevent the
article from moving shall be used.

5.6 Loading Pad — A rigid circular object
200 mm in diameter having a face with a convex
spherical curvature of 300 mm radius and a 12 mm
front edge radius. It shall be constrained to
remain in position without restricting the freedom
of the article to overturn ( see Fig. 4 ). The load-
ing pad shall be attached to a force application
device capable of applying forces with an accuracy
of ±1 N.

Note — A recommended linkage arrangement is
shown in Fig, 5.

5.7 Discs — There shall be a total of 14 discs
each having a radius of 175 mm, thickness of
40 mm and mass of 10 kg.

5.8 Support Apparatus — It shall be used for
carrying out the tests in 7.6.2 to 7.6.4, having a
mass of not more than 2*5 kg.

6. DETERMINATION OF SEAT AND BACK
LOADING POINTS

6.1 Chairs — Position the template ( 5.3 ) with
its load applied at the seat loading point on the
centre line of the chair as far towards the rear as
possible. Adjust its position by pushing the back
loading portion into the back, so levering the seat
portion forward until the shape of the template
correlates with that of the chair ( see Fig. 3 ).
Mark the required loading points from the tem-
plate.

6.2 Stools — Set up the template ( 5.3 ) at an
angle of 90° with the aid of the mark as shown in
Fig. 3. Place the template on the steel as shown
in Fig. 2. Mark the required loading point from
the template.

7. PROCEDURE

7.1 General — Position the chair or stool on the
floor ( 5.4 ) with the legs restrained by stops
( 5.5 ).

7.1.1 For tests on articles with swivelling bases,
rotate the base to the position relative to the seat
that is most likely to cause overturning and tighten

TYPICAL SECTION

A «* seat load ( chairs )

B — back load ( chairs )

C « seat load ( stools )

All dimensions in millimetres.

Fig. 1 Loading Point Template
2

IS t 5416 ( Part 2 ) - 1988

Fig 2 Position of Loading Point

Template

any assembly fittings. Set adjustable height chairs
at the height that is most likely to cause overturn-
ing. Place a chair or stool with a circular base
with its edge against a stop in a position commen-
surate with that specified for four-legged chairs.
Position three or five-star bases so that the two
feet are against the stops ( 5.5 ).

Record whether the article tends to overturn
during each of the tests described in 7.2 to 7.6.

7.2 Forward Overturning and Sideways
Overturning for Chairs Without Arms —

Position the chair with the stops against the front
legs on one side ( as appropriate ). Apply a force
of 600 N vertically by means of the loading pad
( 5.6 ) so as to act at a point 50 mm from the
edge of the seat at those positions along its exposed
periphery most likely to result in instability
( usually tests on the centre line are sufficient ).
Apply a force, F 9 of 20 N horizontally along a
horizontal line extended forwards from the point
where the base of the loading pad meets the upper
surface of the seat ( see Fig. 6 ). Test chairs with
adjustable backrests and reclining and tilting
chairs, with their back assemblies locked or set so
as to be inclined rearwards from the vertical by an

SCALED SQUARE 20*20 mm

Fig. 3 Loading Surface Curves for
Chair Seat and Back Loading Template

angle of 15 ± 5°. Load free swivelling backrests
on the axis of rotation even when this axis cannot
be adjusted by an angle of 15 ± 5°.

c

R12

All dimensions in millimetres.
Fig. 4 Back Loading Pad

IS : 5416 ( Part 2 ) - 1988

LOW FRICTION
BEARINGS

HORIZONTAL
BAR

100 min.

J^r

750 min.

3

c

h = loaded seat height
V = vertical load
F = horizontal force

All dimensions in millimetres.

Fig. 5 Suggested Linkage Arrangement Constraining Loading Pad

600N

600N

50

— F

- — 50

?

~-F

All dimensions in millimetres.
Fig. 6 Forwards Overturning and Sideways Overturning for Chairs Without Arms

7.3 Rearward Overturning

Note — The test applies only to chairs with backs
extending 50 mm or more above the unloaded seat.
This does not apply to tilting chairs or to chairs where
the back reclines beyond those limits-stated in 7.6.1.

7.3.1 Position the chair with the stops against
the rear legs. Apply a vertical force of 600 N to
the seat by means of the loading pad ( 5.6 ) at
the seat loading point ( see 6 and Fig. 7 ). Deter-
mine the distance, h (in mm), between the loaded
seat height and the floor by measuring the
distance between the horizontal bar ( see Fig. 5 )

and the base of the pad, and subtracting it from
the distance between the horizontal bar and the
floor. For chairs having a value of h greater than
720 mm, use an overturning force, F, of 80 N. For
chairs having a value of h less than 720 mm,
calculate the overturning force, F (in N), required
from the following formula:

F = 285-7 ( 1 - A/l 000 )

Apply force F horizontally to the back of the
chair at a height of 300 mm above the unloaded
seat, or at the top edge of the backrest, whichever
is the lower.

IS : 5416 ( Part 2 ) - 1988

Set adjustable angle backrests ( unless they
adjust to such a degree that they are covered
by 7.6.2 or 7.6.3 ) at the rearmost point of their
working range of adjustment. Load articles with
free swivelling backrests on their axis of rotation
even when this axis cannot be set at the rearmost
point of their working range of adjustment.

600N

F ~

Fig. 7

AU dimensions in millimetres.

Rearwards Overturning Under
Loaded Condition

7.3.2 Tilt the chair rearwards about its rear

feet so that the front edge of the seat moves

through a horizontal distance of 100 mm
{ see Fig. 8 ).

Fio. 8

All dimensions in millimetres.

Rearwards Overturning Under
Self Weight

7.4 Sideways Overturning for Chairs with

Arms — Position the chair with the stops ( 5.5 )
against the legs of one side. Apply a vertical force
of 250 N at a point 100 mm to one side of the
fore and aft centre line of the seat and between
\ 75 and 250 mm forward of the rear edge of the
seat ( see Fig. 9 ). Apply a vertical force of 350 N
by means of the loading pad ( 5.6 ) at a position
37 -5 mm inside the outer edge of the arm at the
most adverse position along its length. Apply a
horizontal force, F, of 20 N outwards at the upper
surface of the armrest and in line with the vertical
arm force on the side with stopped feet ( see 4 ).

7.5 Stools — Position the feet of the stool so that
the two feet are resting against the stops ( 5.5 ).
Apply a vertical force of 600 N by means of the
loading pad ( 5.6 ) at a point 50 mm from the

250N

350N

All dimensions in millimetres.

Fig. 9 Sideways Overturning for

Chairs with Arms

edge of the seat nearest the stopped feet
( see Fig. 10 ). Apply a horizontal force, F, of
20 N through the centre of the seat in a direction
towards the stopped feet. Tilt the stool rearwards
about two of its feet so that the front edge of the
seat moves through a horizontal distance of
100 mm.

600N

50

-*- F

All dimensions in millimetres.

Fia. 10 Overturning for Stools
7.6 Rearwards Overturning of Chairs with
Tilting or Reclining Mechanisms

7.6.1 General — The tests in 7.6.2, 7.6.3

and 7.6.4 are applicable to chairs that are fully
reclined or tilted; they are not alternative methods
to those for upright chairs. The test for tilting
chairs is valid for all values of $ ( see Fig. 1 1 ) and
values of y between y »= 90 and 120°. The test is
not required when the minimum value of is
greater than 55°.

IS : 5416 ( Part 2 ) - 1988

Fig. 1 1 Test for Tilting Chairs

The test for reclining chairs without footrests
( 7.6.3 ) is valid for values of 6 ( see Fig. 12 ) less
than or equal to 55° and the test for reclining
chairs with footrests ( 7.6.4 ) is valid for values of
6 ( see Fig. 13 ) less than or equal to 45°.

7.6.2 Tilting Chairs — Place 1 1 discs ( 5.7 ) on
the chair seat firmly settled against the contours
of the back of the chair. If the discs, stacked on
top of each other, exceed the height of the chair
back, it is necessary to use a light stick, or other
means of support, to stop the upper discs from
sliding off. The apparatus of support is shown
in Fig. 14.

All dimensions in millimetres.
Fio. 12 Test for Reclining Chairs Without Footrests

All dimensions in millimetres.
Fig. 13 Test for Reclining Chairs with Footrests

IS : 5416 ( Part 2 ) - 1988

MAXIMUM MASS 2-5 kg

All dimensions in millimetres.
Fxo. 14 Support Apparatus

7.6.3 Reclining Chairs Without Footrests — Set the
chair in its fully reclined position. Determine the
value of 0, the angle between the backrest and the
floor, as illustrated in Fig. 12. Determine the value
of X required [by interpolation of the values in
Table 1, Place eight discs ( 5.7 ) firmly settled
against the contours of the back of the chair at a
point 168 mm above the intersection point of the
seat and back surfaces. Place a further three discs
with their centre at a distance X mm from the
intersection point of the seat and back surfaces as
illustrated in Fig. 12.

7.6.4 Reclining Chairs with Footrests — Garry out
the test described in 7.6.3 except that three discs
shall be position Z mm fr° m ^ intersection

point of the seat and back surfaces ( see Fig. 13 and
Table 1 ).

8. INTERPRETATION OF RESULTS

8.1 Each article shall be considered to have
passed the tests if the article did not overturn
during the tests and if the requirements of the
appropriate product specification are met.

9. TEST REPORT

9.1 The test report shall contain the following
particulars:

a) Details of the article tested, and

b) Whether the article overturns during
testing.

degrees

10
20
30
45
60

TABLE 1 VALUES OF X AND Z

( Clauses 7.6.3 and 7.6.4 )

X

mm

474
424
375
325
252
194

Z
mm

614
564
515
464
392

Note — Intermediate values can be obtained by plotting graph from the values given above.

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